1. Field of the Invention
The present invention relates to a tool transfer system for transferring a tool between two tool holding devices, and more particularly to techniques for facilitating the transfer of a tool between the two tool holding devices.
2. Discussion of Related Art
There is known a tool transfer system for transferring a tool such as a machining tool (e.g., cutting tool, grinding tool) and a plastic working tool (e.g., burnishing tool), between a tool holding shaft and a tool storage device such as a tool magazine, for example, through an automatic tool changer (ATC). JP-2005-14143A (publication of unexamined Japanese Patent Application laid open in 2005) discloses an example of such a tool transfer system in which a tool is held by a tool holding shaft when the tool has been transferred to the tool holding shaft, and is stored in the tool storage device when the tool has been transferred to the tool storage device. In this system, the tool is transferred between the tool holding shaft and the tool storage device while being held by a tool holder. However, there is a case where the tool is transferred while not being held by a tool holder. In this sense, in the following description, a term “tool” will be used as a term generic to a tool held by a tool holder and a tool not held by a tool holder. That is, the term “tool” will be used, without distinguishing a tool held by a tool holder and a tool not held by a tool holder, from each other. Where the term “tool” is used to refer to a tool held by a tool holder, the tool holder may be interpreted as a part of the tool.
A tool disclosed in JP-2005-14143A is equipped with a ball clamping device having a particular arrangement that enables a radially outward flange of a tool holding shaft to be firmly gripped (clamped) from its axially opposite sides by a radially outward flange and a radially inward engaging protrusion of the tool. The radially outward flange extends radially outwardly from a main body (hereinafter referred to as “tool holder body”) of a tool holder of the tool, while the radially inward engaging protrusion protrudes radially inwardly from a tubular-shaped engaging member of the tool, which is fitted on the main body of the tool holder body and which is axially movable relative to the tool holder body and unrotatable relative to the tool holder body. Thus, the tool is fixed to the tool holding shaft by the radially outward flange and the radially inward engaging protrusion of the tool, which cooperate with each other to grip the radially outward flange of the tool holding shaft. A clamp sleeve having a tapered inner circumferential surface is fitted on the tool holder body, and is axially slidable relative to the tool holder body. The tubular-shaped engaging member has a ball retaining hole extending in a radial direction of the tubular-shaped engaging member. The radially outward flange has a tapered surface that is inclined with respect to a plane perpendicular to an axis of the tool holder body. A ball is disposed in the ball retaining hole of the tubular-shaped engaging member, and is movable in the radial direction. A spring is disposed between the clamp sleeve and the tool holder body, and forces the clamp sleeve in a backward direction, i.e., a direction away from an axially distal end of the tool holder body toward an axially proximal end of the tool holder body.
In this clamping device, as a result of the backward movement of the clamp sleeve owing to force of the spring, the ball is forced by the tapered inner circumferential surface of the clamp sleeve, inwardly in the radial direction. The ball, which is thus forced inwardly in the radial direction, is forced into a wedge-shaped gap that is defined by an inner circumferential surface of the ball retaining hole of the tubular-shaped engaging member and the tapered surface of the radially outward flange, whereby the tubular-shaped engaging member is moved relative to the tool holder body in a forward direction, i.e., a direction away from the axially proximal end of the tool holder body toward the axially distal end of the tool holder body. As a result of the forward movement of the tubular-shaped engaging member relative to the tool holder body, the radially outward flange of the tool holding shaft is firmly gripped by the radially outward flange of the tool holder body and the radially inward engaging protrusion of the tubular-shaped engaging member. It should be noted that, for enabling the radially outward flange of the tool holding shaft to be positioned between the radially outward flange of the tool holder body and the radially inward engaging protrusion of the tubular-shaped engaging member, there is required means for permitting the radially outward flange of the tool holding shaft to pass through the radially inward engaging protrusion of the tubular-shaped engaging member, namely, permitting the radially inward engaging protrusion of the tubular-shaped engaging member to pass through the radially outward flange of the tool holding shaft. To this end, the radially outward flange of the tool holding shaft has a cutout extending over an entire axial length of the radially outward flange. In this arrangement, the tool holding shaft has to be positioned relative to the tool in a predetermined angular position that permits the radially inward engaging protrusion of the tubular-shaped engaging member to pass through the cutout of the radially outward flange of the tool holding shaft so as to be moved from an axially distal side of the radially outward flange to an axially proximal side of the radially outward flange. After the radially inward engaging protrusion of the tubular-shaped engaging member having passed through the cutout of the radially outward flange of the tool holding shaft, namely, after the tool has been introduced into the tool holding shaft, the tool holding shaft is rotated relative to the tool by a predetermined angle, whereby the tubular-shaped engaging member is moved relative to the tool holder body in the forward direction. As a result of the forward movement of the tubular-shaped engaging member relative to the tool holder body, the radially outward flange of the tool holding shaft is firmly gripped by the radially outward flange of the tool holder body and the radially inward engaging protrusion of the tubular-shaped engaging member. This clamping device requires a device for rotating the tool holding shaft relative to the tool and also a device for controlling an angular position of the tool holding shaft relative to the tool, although redundant description of these devices is not provided herein.
In the above arrangement disclosed in JP-2005-14143A, when the tool is to transferred from the tool storage device to the tool holding shaft, the tool holding shaft is first positioned in a coaxial position in which a tool receiving hole of the tool holding shaft is axially opposed to and coaxial with a tool receiving hole of the tool storage device. Then, the tool holding shaft is moved toward the tool storage device with the tool holding shaft being positioned in the above-described predetermined angular position relative to the tool, whereby the tool is received into the tool receiving hole of the tool holding shaft, while the clamp sleeve is moved in the forward direction against force of the spring. Then, with the tool holding shaft being rotated by the above-described predetermined angle relative to the tool, the clamp sleeve is moved in the backward direction owing to the force of the spring, so as to be positioned in a clamping position, whereby the radially outward flange of the tool holding shaft is gripped by the radially outward flange of the tool holder body and the radially inward engaging protrusion of the tubular-shaped engaging member. Thus, the tool is firmly held by the tool holding shaft. When the tool is to be transferred from the tool holding shaft to the tool storage device, too, the tool holding shaft and the tool storage device are moved toward and away from each other and rotated relative to each other.
As described above, in the tool transfer system disclosed in JP-2005-14143A, the tool can be automatically transferred between the tool holding shaft and the tool storage device. However, for the transference of the tool between the tool holding shaft and the tool storage device, the tool holding shaft has be to axially moved and also rotated about an axis of the tool receiving hole of the tool holding shaft, thereby complicating control of movement of the tool holding shaft and also construction of the tool (more precisely, construction of the tool holder body).